Lens should not access Banshee's sqlite database

[Bertrand Lorentz]

The Lens currently open banshee.db directly on startup.
This might be a problem for several reasons:
 - We might change the database structure
 - sqlite doesn't support multiple processes accessing the same database file, and Banshee might be started while the Lens accesses the database.

The alternative would be to use the various org.bansheeproject.CollectionIndexer.* interfaces described in this page:
http://banshee.fm/contribute/write-code/dbus-interfaces/

The GNOME Do plugin already uses it, so it might help to have a look at it:
http://bazaar.launchpad.net/~do-plugins/do-plugins/trunk/files/head:/Banshee/src/

This approach would also allow the Lens to show tracks right after they've been added in Banshee

[Chow Loong Jin (hyperair)]

Here's a crash log after Banshee got locked out of its own database. lsof showed only /usr/lib/unity-lens-music/unity-music-daemon accessing it.